A display device used in an electronic apparatus, particularly a mobile apparatus frequently used outdoors, e.g. a car navigation device, a mobile phone, etc., is generally equipped with a display device which exhibits an illumination-adjusting function for adjusting display illuminance according to the intensity of ambient light. For example, the PCT Japanese Patent Publication No. 2001-522058 discloses a display system which includes an illumination controller capable of changing display illuminance according to ambient light detected by an ambient light photo sensor. With the adjustment, illuminance is increased in bright places such as outdoors in the daytime and decreased in dark places such as indoors in the nighttime.